Tank and work-holder apparatus for liquid coating for honeycomb structure

ABSTRACT

A liquid coating method for coating a liquid onto inner cells of a honeycomb structure includes the steps of supplying a liquid to the inside of a honeycomb structure vertically arranged from its lower part to cause the liquid to adhere to the inner cells therein, and supplying pressurized air to an upper part of the honeycomb structure to discharge the liquid within the inner cells. A holding apparatus for holding an article includes an outer cylinder in a form of a pipe having an inner wall with an inner diameter which allows an article to be held to pass therethough easily and which has a sufficient strength, a resilient tube having an inner diameter which prevents the article to be held from passing therethough under no tension and having ends each sealingly connected to the outer cylinder, thus defining together with the inner wall of the outer cylinder a sealed space therebetween, means for discharging a fluid from the sealed space; and means for supplying the fluid to the sealed space.

This application is a continuation of Ser. No. 07/893,078 filed Jun. 2,1992, now U.S. Pat. No. 5,422,138 which is a division of Serial No.07/614,629 filed Nov. 16, 1990, now U.S. Pat. No. 5,182,140.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for coatinghoneycomb structures. More particularly, the present invention relatesto a coating method and a coating apparatus for causing a fluid such asa slurry to adhere to inner cells of honeycomb structures for use, forexample, in treating exhaust gas of cars. The present invention alsorelates to a holding method and a holding apparatus which can be usedadvantageously in the coating method and coating apparatus of thepresent invention.

BACKGROUND AND PRIOR ART OF THE INVENTION

For the treatment of exhaust gas from cars and the like, there has beenknown a method in which catalysts are carried in honeycomb structuresmade of metal or ceramics.

Various types of honeycomb structures have been proposed. For example,one of the known honeycomb structures has a large number of inner cellsinside thereof which extend longitudinally along the length of thehoneycomb structure and have open ends on both sides thereof. Anothertype of the known honeycomb structure also has a large number oflongitudinally arranged cells inside thereof which have an open end onone side and a closed end on the other side thereof, and are arrangedalternately so that every other adjacent cell has an open end (or aclosed end) on one side and a closed end (or an open end) on the otherside of the honeycomb structure and communicate with each other throughholes in the walls of the cells.

In order to have catalyst components carried on the walls of the cellsof the honeycomb structure of the above-described type in a suitablemanner, it is necessary to coat various liquids including, among others,a slurry which contains catalyst components on the walls of the cells.

Examples of the liquids to be applied to the walls of the cells are asfollows.

(a) Chemicals to be used in pretreatment of post-treatment in theproduction of catalysts, for example, acids, aqueous alkali solutions,and organic substances. These are aqueous solutions which contain nocatalyst component.

(b) Aqueous solutions containing catalyst components such as aqueoussolutions of palladium compounds, aqueous solutions of platinumcompounds, and aqueous solutions of rhodium compounds.

(c) Slurries containing catalyst components and mainly composed ofcatalyst components such as platinum, palladium and rhodium, refractorymetal oxides such as aluminum oxide and cerium oxide. The slurries maycontain one or more of various metal compounds, acids, organicsubstances, and the like. Generally, the slurries have a high viscosity(e.g., on the order of from 100 to 500 cps), a specific gravity of from1.0 to 2.0 g/ml, and a component particle size of no greater than 10 μm.

(d) Slurries mainly composed of refractory metal oxides such as aluminumoxide and cerium oxide. The slurries may contain one or more of variousmetal compounds, acids, organic substances and the like. They contain nocatalyst component represented by precious metals. Their physicalcharacteristics are the same as the slurries described in (c) above.

As a coating method for applying the above-described various liquids tothe walls of numerous cells in the honeycomb structure having theconstruction described above, a method has been used in which ahoneycomb structure in a vertical position is dipped in a desired liquidcontained in a storage tank, the honeycomb structure is then taken outfrom the liquid bath and left to stand as is for a while to extract orseparate the liquid from the honeycomb structure by free fall of theliquid, and the liquid still remaining in the cells is removed forciblyby an air-knife which blasts high-pressure air.

However, the conventional method has the following problems.

Firstly, it takes a considerably long time for the liquid to adhere allover the walls of the inner cells in the honeycomb structure, whichmakes it difficult to carry out the treatment efficiently. The cellshave a considerably small sectional area and the pressure posed on theliquid while it rises within the cell is generated by the differencebetween the level of the liquid surface in the storage tank and that ofthe liquid surface in the cell. Hence, this pressure is not so high. Inaddition, usually the liquid to be coated has a high viscosity.Therefore, in the above-described method, the speed at which the liquidrises within the cells is not high enough.

Secondly, the amount of the liquid which adheres to the wall of thecells is not equal from cell to cell. Upon the separation of the liquid,the liquid is left to fall free followed by the removal of the liquidwhich is carried out by using an air-knife. As a result, it is often thecase that a large amount of the liquid remains in some cells while onlya small amount of the liquid remains in other cells, thus failing tocause the liquid to adhere to the honeycomb structure uniformly. It isdesirable and important to uniformly distribute catalyst components andthe like on the walls of the inner cells in the honeycomb structurebecause in the case of the treatment of exhaust gas, for example, thereaction occurs when the exhaust gas contacts the catalyst component onthe honeycomb structure

Thirdly, unnecessary liquid adheres to the side surface of the honeycombstructure. The right portion where liquid is to adhere is the walls ofthe inner cells in the honeycomb structure through which the exhaust gaspasses, but it is unnecessary to allow the liquid to adhere on the sidesurface of the honeycomb structure. The liquid adhering on the sidesurface is of no use.

As described hereinbelow, in the liquid coating method and apparatus forthe honeycomb structure of the present invention, a honeycomb structure,which is an article to be held, having a shape of a circular column, anelliptic column, a circular cylinder, an elliptic cylinder, or the like,must be held and the outer periphery of the article to be held must becovered partly or entirely.

For this purpose, a holder can be used which is composed of two halves,each having a shape of a longitudinally split circular cylinder providedwith a recess or groove that defines an inner cavity having a contourcorresponding to that of the article to be held when the halves are puttogether in close contact with each other.

However, if the size and shape of the article to be held, i.e.,honeycomb structure, fluctuate, a problem arises that when the articleto be held is relatively large, the holder is closed incompletely tofail to establish a complete seal, and on the other hand, when thearticle to be held is relatively small, it does not contact the holderclosely, resulting in that the force of holding given by the holder isnot strong enough.

A method and an apparatus might be considered useful in which articlesto be held are held by using a rubber tube having an inner diametersufficiently larger than the outer diameters of the articles to be held,and air is forcibly introduced into the tube to reduce its innerdiameter to hold the articles in close contact therewith.

However, in the above-described apparatus, a problem arises that whenair is introduced into the rubber tube, wrinkles tend to occur in therubber from part to part, resulting in that the sealing of those partswith wrinkles is incomplete.

For example, when it is contemplated to coat a liquid on an insidesurface of an article to be held having a shape of a circular cylinderand provided only inside thereof with one or more tubes extending in anaxial direction, as honeycomb structure, the article to be held is heldby a holder, a liquid tank is coupled with the lower end of the article,and a liquid is supplied from the liquid tank and forced to rise intothe inside of the article to coat the liquid only on the inside thereof.In this case, the use of the conventional holder with a rubber tuberesults in the occurrence of wrinkles in the rubber as earlierexplained, and the liquid forced upward flows upward between the articleand the rubber tube via channels formed by the wrinkles and thus theliquid adheres also to the outside of the article, thus failing toachieve the purpose.

The conventional technique suffers from a problem that when the size andshape of the article to be held fluctuate more or less, it is difficultto hold the article certainly and, in addition the seal between thearticle and the holder is insufficient.

SUMMARY OF THE INVENTION

In order to solve the above-described problems, the present inventionprovides a liquid coating method for coating a liquid in inner cells ina honeycomb structure, comprising the steps of:

supplying a liquid to an inside of a honeycomb structure verticallyarranged from its lower part to cause the liquid to adhere to the innercells; and

supplying pressurized air to an upper part of the honeycomb structure todischarge the liquid within the inner cells.

According to the method of the present invention a liquid to be coatedis introduced into the inside of a honeycomb structure arrangedvertically from its lower part so that the liquid to be coated canadhere to the inner cells of the honeycomb structure. Then, pressurizedair is supplied to the upper part of the honeycomb structure todischarge liquid which remains within the inner cells. Thus, the liquidis introduced forcibly from below and discharged or expelled bypressurized air. This makes it possible to cause the liquid to adherespeedily and uniformly without causing the liquid to adhere to the sidesurface of the honeycomb structure.

According to a preferred embodiment of the present invention, theabove-described method comprises the steps of:

providing a liquid storage tank for storing a liquid to be coated, theliquid storage tank having an upper opening at its upper part and an airdischarge outlet, and an air duct having a lower opening at its lowerpart;

connecting the upper opening of the liquid storage tank to a bottom ofthe honeycomb structure vertically arranged;

further connecting the lower opening of the air duct to a top of thehoneycomb structure, and

supplying the liquid to be coated from the liquid storage tank into theinner cells in the honeycomb structure to cause the liquid to adhere tothe inner cells.

Further, according to another preferred embodiment of the presentinvention, the method comprises the steps of supplying pressurized airfrom the air duct to the upper part of the honeycomb structure anddischarging the pressurized air from the air discharge outlet of theliquid storage tank to discharge the liquid in the cell.

As described above, according to the preferred embodiments of thepresent invention, a liquid storage tank having an upper opening and anair discharge outlet, and an air duct having a lower opening areprovided. A honeycomb structure vertically arranged is connected at itsbottom to the upper opening of the storage tank, and at its top to thelower opening of the air duct. The liquid to be coated is supplied fromthe liquid storage tank into the inner cells of the honeycomb structure.By doing so, the liquid to be coated is caused to adhere to the innercells. Then, pressurized air is supplied to the upper part of thehoneycomb structure from the air duct and the pressurized air isdischarged from the air discharge outlet of the liquid storage tank sothat the liquid within the cells can be discharged. As a result, theliquid can be caused to adhere to the inner cells speedily anduniformly, thus enabling coating treatment without causing the liquid toadhere to the side surface of the honeycomb structure.

Furthermore, in order to solve the above-described problems, the presentinvention provides a liquid coating apparatus for coating a liquid onwalls of inner cells in a honeycomb structure, comprising:

a liquid storage tank for storing a liquid to be coated, the storagetank having an upper opening and an air discharge outlet;

an air duct for supplying an air stream, the air duct having a loweropening;

a first sealing element for sealingly connecting a bottom of thehoneycomb structure to the upper opening of the liquid storage tank;

a second sealing element for sealingly connecting a top of the honeycombstructure to the lower opening of the air duct; and

means for raising the liquid in the liquid storage tank through theupper opening and the inner cells in the honeycomb structure. The liquidcoating apparatus of the present invention includes a liquid storagetank for storing a liquid to be coated, which has an upper opening atits upper part and an air discharge outlet, and an air duct forsupplying an air stream, which has a lower opening at its lower part.The bottom of the honeycomb structure is sealingly connected to theupper opening of the liquid storage tank by a first sealing element. Onthe other hand, the top of the honeycomb structure is sealinglyconnected to the lower part opening of the air duct by a second sealingelement. The liquid in the liquid storage tank is raised by a device forraising the liquid through the upper opening and the inner cells in thehoneycomb structure. On the other hand, pressurized air is supplied fromthe top of the honeycomb structure by the air duct. This constructionmakes it possible to cause the liquid to be coated to adhere speedilyand uniformly to the target and thus carry out the coating treatmentwithout causing the liquid to adhere to the side surface of thehoneycomb structure.

In addition, in order to solve the above-described problems, the presentinvention provides a liquid coating apparatus for coating a liquid onwalls of inner cells in a honeycomb structure, comprising:

a liquid storage tank having a first tank sealed from outside, and asecond tank having an upper opening which is adapted to be communicatewith a bottom of a honeycomb structure and a communication opening whichcommunicates with a lower part of the first tank; and

an air supplier for supplying pressurized air to an upper part of thefirst tank.

The apparatus according to the above-described embodiment of the presentinvention includes a liquid storage tank which has first and secondtanks. The first tank is sealed from the outside, and the second tankhas an upper opening at its upper part. The air supplier suppliespressurized air to the upper part of the first tank. As a result, theliquid rises in the second tank and in the inside of the honeycombstructure. This construction makes it possible to cause the liquid toadhere speedily and uniformly and thus carry out the liquid coatingwithout causing the liquid to adhere to the side surface of thehoneycomb structure.

According to another embodiment, in order to solve the above-describedproblems, the present invention provides an apparatus for holding anarticle, comprising:

an outer cylinder in a form of a pipe having an inner wall with an innerdiameter which allows an article to be held to pass therethrough easilyand which has a sufficient strength;

a resilient tube having an inner diameter which prevents the article tobe held from passing therethrough under no tension and having ends eachsealingly connected to the outer cylinder, thus defining together withthe inner wall of the outer cylinder a sealed space therebetween,

means for discharging a fluid from the sealed space; and

means for supplying the fluid to the sealed space.

Still further, in order to solve the above-described problems, thepresent invention provides a method for holding an article using aresilient tube, comprising the steps of:

forcibly increasing an inner diameter of a resilient tube, the innerdiameter preventing an article to be held from passing therethroughunder no tension by discharging fluid in a sealed space defined betweenthe resilient tube and an outer cylinder outside the resilient tube,

arranging the article in the resilient tube with increased innerdiameter, and

supplying the fluid to the space to decrease the inner diameter of theresilient tube to hold the article.

The method and apparatus for holding an article according to the presentinvention enable articles having a shape of a circular column, anelliptic column, a circular column, a circular cylinder or the likecontour, such as a honeycomb structure, to be held particularlysuitably. The articles to be held include solid articles such as columnsand hollow ones such as cylinders with open ends, those having insidethereof one or more tubes extending axially. However, the outer shapeand inner construction of the articles to be held are not limited tothose described above, but those articles having square, triangular orthe like shapes in cross section can also be held.

The outer cylinder is provided with a resilient tube as explainedhereinbelow having an inner diameter which allows articles to be held orinserted therein. The outer cylinder may be have various cross-sectionalshapes such as circular, elliptic, square and the like shapes inaccordance with the cross-sectional shape of the article to be held.

The outer cylinder-must have a sufficient strength for supporting theresilient tube.

The resilient tube may be made of, for example, natural rubber,synthetic rubber or the like. The resilient tube under no tension, i.e.,in a relaxed state, has an inner diameter smaller than the outer shapeor contour of the article to be held.

The resilient tube is arranged inside the outer cylinder, and both endsof the resilient tube are sealingly connected to the end surface, outerwall or inner wall of the outer cylinder so that a sealed space can bedefined between the resilient tube and the inner wall of the outercylinder.

The discharge means may be constructed, for example, by a vacuum pump,and a piping connecting the vacuum pump to the sealed space, andoperates to discharge the fluid in the sealed space, for example, air ornitrogen.

The supply means may be constructed, for example, by a valve whichcontrols the communication between the sealed space and the outside. Thesupply means applies, for example, the outside atmospheric pressure tothe sealed space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the liquid coating apparatus for thehoneycomb structure according to a preferred embodiment of the presentinvention;

FIG. 2 is a schematic diagram of the holding apparatus used in theliquid coating apparatus illustrated in FIG. 1;

FIGS. 3 to 6 are each a schematic diagram illustrating the operation ofthe liquid coating apparatus illustrated in FIG. 1;

FIG. 7 is a schematic perspective view of the apparatus for measuringthe fluctuation of value B measured in Example 3, showing the positionat which value B is measured;

FIG. 8 is a perspective view of the holding apparatus using a resilienttube according to a preferred embodiment of the present invention;

FIG. 9a is a plan view of the main parts of the apparatus illustrated inFIG. 8 before its operation starts;

FIG. 9b is a central cross-sectional view of the apparatus illustratedin FIG. 1 before its operation starts.

FIG. 10a is a plan view of the main parts of the apparatus illustratedin FIG. 8 in a state where the liquid in the sealed space has beendischarged;

FIG. 10b is a central cross-sectional view of the apparatus illustratedin FIG. 8 in a state where the liquid in the sealed space has beendischarged;

FIG. 11a is a plan view of the main parts of the apparatus illustratedin FIG. 8 in a state where the article to be held is arranged in theinside thereof;

FIG. 11b is a central cross-sectional view of the apparatus illustratedin FIG. 8 in a state where the article to be held is arranged in theinside thereof;

FIG. 12a is a plan view of the main parts of the apparatus illustratedin FIG. 8 in a state where atmospheric pressure has been applied to thesealed space;

FIG. 12b is a central cross-sectional view of the apparatus illustratedin FIG. 8 in a state where atmospheric pressure has been applied to thesealed space;

FIG. 13a is a plan view of the main parts of the apparatus illustratedin FIG. 8 in a state where pressurized air has been applied to thesealed space;

FIG. 13b is a central cross-sectional view of the apparatus illustratedin FIG. 8 in a state where pressurized air has been applied to thesealed space;

FIG. 14a is a plan view of the main parts of the holding apparatusaccording to a variation of the present invention in which the outercylinder has an elliptic cross section and the resilient tube has acircular cross section;

FIG. 14b is a central cross-sectional view of the holding apparatusaccording to a variation of the present invention in which the outercylinder has an elliptic cross section and the resilient tube has acircular cross section;

FIG. 15a is a plan view of the main parts of the holding apparatusaccording to another variation of the present invention in which theouter cylinder has a circular cross section and the resilient tube hasan elliptic cross section;

FIG. 15b is a central cross-sectional view of the holding apparatusaccording to another variation of the present invention in which theouter cylinder has a circular cross section and the resilient tube hasan elliptic cross section;

FIG. 16a a plan view of the main parts of the holding apparatusaccording to still another variation of the present invention in whichboth the outer cylinder and resilient tube, respectively, have acircular cross section and the resilient tube has an elliptic crosssection;

FIG. 16b is a central cross-sectional view of the holding apparatusaccording to still another variation of the present invention in whichboth the outer cylinder and resilient tube, respectively, have acircular cross section;

FIG. 17a is a plan view of the main parts of the conventional holdingapparatus as comparison in a state where the article to be held has beenarranged in the inside thereof;

FIG. 17b is a central cross-sectional view of the conventional holdingapparatus as comparison in a state where the article to be held has beenarranged in the inside thereof;

FIG. 18a is a plan view of the main parts of the conventional holdingapparatus illustrated in FIG. 7a, showing the state of holding; and

FIG. 18b is a central cross-sectional view of the conventional holdingapparatus as illustrated in FIG. 17b, showing the state of holding.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, referring to the attached drawings, the coating apparatus andmethod according to preferred embodiments of the present invention willbe described in greater detail hereinbelow.

While the embodiments described below relate to a coating apparatus andmethod for coating a slurry containing catalyst components onto ahoneycomb structure having a shape of a circular cylinder, it will beapparent that various modifications or variations which are obvious tothe skilled artisan may be made on the embodiments, if desired, ontomodify them to a coating apparatus and method for coating variousliquids such as those described above on to honeycomb structures havingvarious shapes and forms.

The coating apparatus for a honeycomb structure illustrated in FIG. 1includes a liquid storage tank 10, a slurry storage device 12 from whicha slurry is supplied to the liquid storage tank 10, an air supply device14 which supplies pressurized air to the liquid storage tank 10, airduct 16, an air control device 18 which controls the supply of thepressurized air from a pressurized air source A to the air duct 16, aholding device 22 for sealingly supporting a honeycomb structure 20between the liquid storage tank 10 and the air duct 16, a cyclone device24, connected to the liquid storage tank 10, and a gravimetric device 25for measuring the weight of, for example, the liquid storage tank 10containing slurry therein.

The liquid storage tank 10 has a first tank, i.e., an outer tank 26,second tank, i.e., an inner tank 28, and a stirrer 30 for renderinguniform the density of the slurry in the outer tank 26, and retains apredetermined amount of the slurry therein.

The outer tank 26 has on its upper part an air supply port 32 whichcommunicates to the air supply device 14. The upper part of the outertank 26 is sealed from the outside so that air in the upper part of theouter tank 26 will not leak to the outside.

The outer tank 26 has on its lower part a slurry supply port 34 whichcommunicates with the slurry supply device 12 and a discharge port 36having a valve which is usually closed.

The inner tank 28 has on its upper part a horizontally extending upperwall 38 which defines an upper opening 40, and an air discharge port 42which communicates with the cyclone device 24, and on its lower part acommunication port 44 which communicates with the outer tank 26.

Because the liquid storage tank 10 has the above-described construction,the supply of a predetermined amount of pressurized air from the airsupply device 14 to the liquid storage tank 10 through the air supplyport 32 increases the pressure of the air in the upper part of the outertank 26, which in turn increases the level of the slurry in the innertank 28, resulting in that the slurry rises to a predetermined levelabove the upper end surface of the honeycomb structure 20 as describedbelow. In order to supply a sufficient amount of the slurry from theouter tank 26 to the inner tank 28, the horizontal sectional area of theouter tank 26 is preferably sufficiently larger than the horizontalsectional area of the inner tank 28 and the communication port 44 of theinner tank 28 opens downward.

In this embodiment, the height to which the slurry is caused to risedepends on the amount of the slurry in the liquid storage tank 10 andthe amount of the pressurized air supplied from the air supply device12. For example, the level to which the liquid surface of the slurry hasrisen may be detected by providing a detector in the air duct 16.Alternatively, it is possible to supply a predetermined amount of theslurry, instead of the pressurized air, to the liquid storage tank 10and determine the level to which the liquid surface of the slurry iscaused to rise.

The slurry storage device 12 has a slurry tank 46 for storing theslurry, stirrer 47, a pump 48 and a control valve 50, and controls theamount of the slurry supplied from the slurry tank 46 to the liquidstorage tank 10 by means of the pump 48 and the control valve 50.

The control valve 50 of the slurry supply device 12 and the slurrysupply port 34 of the liquid storage tank 10 are connected to each otherwith a flexible tube 52.

It is preferred to construct the apparatus such that the pump 48 and thecontrol valve 50 can be controlled by signals issued from thegravimetric device 25, for example, as described below in order for agiven amount of the slurry to be retained before the coating operationstarts.

The air supply device 14 has an air chamber 54 to which pressurized airis supplied from the pressurized air source A, an air pump 56 connectedto the air chamber 54, a control valve 58, and a exhaust valve 59 fordischarge changing the air in the upper part of the outer tank 26 of theair duct 16.

The air pump 56 further pressurizes the pressurized air supplied fromthe air chamber 54 and supplies it to the control valve 58.

The control valve 58 is opened or closed by a control device (not shown)or manually. The control valve 58 and the exhaust valve 59 are connectedto the air supply port of the liquid storage tank 10 through a flexibletube 60.

When the air pump 56 is actuated to open the control valve 58, thepressurized air is supplied from the control valve 58 to the upper partof the outer tank 26 through the air supply port 32. As a result, theslurry in the inner tank 28 is caused to rise as described above andrise further through the upper opening 40 of the liquid storage tank 10and the inside of the honeycomb structure 20.

As another device for causing the slurry to rise, there can be used, forexample, a pump for injecting the slurry to the liquid storage tank 10,or a device which includes a part of the outer wall of the liquidstorage tank which is constructed by a flexible material capable ofbeing deformed so as to reduce the inside volume of the liquid storagetank.

The air duct 16 is arranged above the liquid storage tank 10 and has anair inlet port 61 and a lower opening 62 arranged as opposing the upperopening 40 of the liquid storage tank 10. The air duct 16 has an innerspace of a considerably large volume so that the air stream can bedischarged from the lower opening 62 at a constant pressure.

The air duct 16 has also a horizontally extending flange-shaped lowerwall 64 on the lower part thereof, which can move slightly up and downso that the holding device 22 can be arranged sealingly between theliquid storage tank 10 and the air duct 16.

The air control device 18 has a control valve 65 and an exhaust valve66, and supplies pressurized air at a predetermined pressure at apredetermined timing to the air duct 16 by means of a control device(not shown) or manually to discharge the pressurized gas in the air duct16. The air control device 18 may have a pressure control device (notshown) and an additional passage or channel (not shown) to the air duct16, if desired, in order to supply a desired pressurized air to the airduct 16.

The exhaust valve 66 of the air control device 18 and the air inlet port61 of the air duct 16 are connected to each other with a flexible tube67.

The holding device 22 has a shape of a circular cylinder having an innerhole of a circular column in shape. The holding device is composed oftwo splittable parts, or halves, as shown in FIG. 2. The two halves maybe connected to each other with a connecting device (not shown) andarranged so that the inner side surface of the holding device 22 canclosely contact the side surface of the honeycomb structure 20. Ofcourse, the holding device 22 may be divided into three, four or moreparts instead of two parts.

It is preferred that the holding device 22 be made of a material whichis hard to deform and has resistance to chemicals, such as MC nylon.Further, the holding device 22 may be provided with a sheet of solid orporous, i.e., spongy rubber having a thickness on the order of from 1 to5 mm on its upper surface, lower surface and inner side surface in orderto increase its sealing ability.

The diameter of the inner hole of the holding device 22, i.e., the outerdiameter of the honeycomb structure 20, is smaller than the diameter ofthe upper opening 40 of the liquid storage tank 10 and that of the loweropening 62 of the air duct 16. On the other hand, the outer diameter ofthe holding device 22, i.e., the diameter of the outer side wall, islarger than the diameter of the upper opening 40 of the liquid storagetank 10 and that of the lower opening 62 of the air duct 16. Because ofthis construction, when the slurry is urged upward to above the liquidstorage tank 10, the slurry comes to rise through all the cells in thehoneycomb structure 20. Alternatively, the slurry can be caused to risethrough all the cells in the honeycomb structure 20 even when the outerdiameter of the honeycomb structure 20 is larger than the diameter ofthe upper opening 40 of the liquid storage tank 10 and that of the loweropening 62 of the air duct 16, if the honeycomb structure 20 issupported in a mid position of the holding device 22, for example, usingthe holding device 22 of a large height instead of using theabove-described construction.

The holding device 22 is arranged so that its inner side surface canclosely contact the side surface of the honeycomb structure 20, and theholding device 22 thus arranged is positioned between the liquid storagetank 10 and the air duct 16 after raising the air duct 16 to someextent. Then, by lowering the air duct 16, the honeycomb structure 20 isset to the position as illustrated in FIG. 1. In this position, thelower surface of the holding device 22 sealingly contacts the upper wall38 of the liquid storage tank 10, and the upper surface of the holdingdevice 22 sealingly contacts the lower wall 64 of the air duct 16. Theinner side surface of the holding device 22 sealingly contacts the sidesurface of the honeycomb structure 22. With this construction, when theslurry is pushed up to above the liquid storage tank 10, the slurryrises through the inner cells of the honeycomb structure 20 withoutcausing leakage of the slurry to the outside between the lower surfaceof the holding device 22 and the upper wall 38 of the liquid storagetank 10 as well as between the upper surface of the holding device 22and the lower wall 64 of the air duct 16, and without rising between theinner side surface of the holding device 22 and the side surface of thehoneycomb structure 20.

As described above the holding device 22 includes the first sealingelement for sealingly connecting the liquid storage tank 10 to thehoneycomb structure 20, and the second element for sealingly connectingthe air duct 16 to the honeycomb structure 20, integrally assembled witheach other. These sealing elements may be of any type so far as theyhave the above-described function but are limited in no way to thoseillustrated in the attached drawings. For example, it may be constructedsuch that the upper and lower sealing elements are connected to eachother with a connection rod, with the upper sealing element sealinglycontacting the lower wall 64 of the air duct 16 and the side surface ofthe honeycomb structure 20, and on the other hand, the lower sealingelement sealingly contacting the upper wall 38 of the liquid storagetank 10 and the side surface of the honeycomb structure 20.

Alternatively, the upper and lower sealing elements may be supported bythe lower wall 64 of the air duct 16 and the upper wall 38 of the liquidstorage tank 10, respectively, without using the connection rod.

The cyclone device 24 has an air inlet port 68 connected to the airdischarge port 42 of the liquid storage tank 10, a gas componentdischarge port 70 provided with a control valve 69, and a liquidcomponent discharge port 72 provided with a control valve 71. Thecyclone device 24 separates the pressurized air containing a liquidcomponent such as slurry supplied from the air discharge port 42 of theliquid storage tank 10 into gas components and liquid components, anddischarges them through the gas component discharge port 70 and theliquid component discharge port 72, respectively.

The air inlet port 68 of the cyclone device 24 and the air dischargeport 42 of the liquid storage tank 10 are connected to each other with aflexible tube 74.

The gravimetric device 25 is provided under the liquid storage tank 10,and measures the total weight of the liquid storage tank 10 itself andof the slurry contained therein. From this, the amount of the slurry inthe liquid storage tank 10 can be known. That is, as described earlier,the control valve 50 of the slurry storage device 12 and the slurrysupply port 34 of the liquid storage tank 10 are connected to each otherwith the flexible tube 52; the control valve 58 and the exhaust valve ofthe air supply device 14 are connected to the air supply port 32 of theliquid storage tank 10 with the flexible tube 60; and further, the airinlet port 68 of the cyclone device 24 is connected to the air dischargeport 42 of the liquid storage tank 10 with the flexible tube 74; hencethe weight of the liquid storage tank 10 itself and the weight of theslurry in the tank 10 are posed on the gravimetric device 25.

Before starting the coating operation, the amount of the slurry in theliquid storage tank 10 is measured using the gravimetric device 25, andthe pump 48 and the control valve 50 of the slurry storage device 12 areactuated in accordance with the measured amount to supply apredetermined amount of the slurry to the liquid storage tank 10 so thata constant amount of the slurry can always be retained in the liquidstorage tank 10 before the coating operation starts.

Now, referring to FIGS. 3 to 6, the operation of the liquid coatingapparatus illustrated in FIG. 1 is explained.

At first, the honeycomb structure 20 and the holding device 22 aresealingly arranged between the liquid storage tank 10 and the air duct16 as illustrated in FIG. 3, and the amount of the slurry is measured bymeans of the gravimetric device 25, with replenishing the slurry fromthe slurry storage device 12 so that a predetermined amount of theslurry can be retained in the liquid storage tank 10, and then thecontrol valve 50 of the slurry storage device 12 is closed (cf. FIG. 1).

Next, as illustrated in FIG. 3, a predetermined amount of pressurizedair is supplied from the air supply device 14 to the upper part of theouter tank 26 through the air supply port 32 to lower the level of theliquid surface in the outer tank 26, to elevate the level of the liquidsurface in the inner tank 28, and then adjust the level of the slurry toa position above the upper end surface of the honeycomb structure 20.

The pressure in the air duct 16 is retained substantially at atmosphericpressure by means of the exhaust valve 66 of the air control device 18,which causes the slurry to rise through the inner cells in the honeycombstructure 20 so that the level of the liquid surface can reach aposition higher than the upper end surface of the honeycomb structure 20when the pressurized air is supplied as described above.

After completion of the supply of the pressurized air from the airsupply device 14 to the upper part of the outer tank 26, it is preferredto retain that state for a while, for example, for from 1 to 10 seconds.This is sometimes necessary, for example, in the case where the slurryhas a high viscosity, the speed of slurry rising in the honeycombstructure 20 is low and thus it is necessary to await until the liquidsurface reaches a position higher than the upper end surface of thehoneycomb structure 20 completely.

The speed at which the slurry rises in the honeycomb structure 20 ispreferably from 5 to 20 cm/sec. If this speed is too high, speeds atwhich the slurry rise in a great number of cells in the honeycombstructure differ from cell to cell, and therefore, there is apossibility that in some cells the coating treatment is performed in astate in which the slurry rises insufficiently. On the other hand, ifthe speed is too low, the efficiency of the coating operation isaggravated.

In order for the slurry to adhere to all of the plurality of cells inthe honeycomb structure 20 all over the entire lengths of the respectivecells, it is preferred to cause the slurry to rise so that the level ofthe liquid surface of the slurry can reach to a position higher, forexample, by from 0.5 to 10 cm than the upper end surface of thehoneycomb structure 20. This preferred height of the slurry variesdepending on the density, length, shape and the like factors of thecells and generally higher density of the cells gives higher level ofthe liquid surface. Particularly preferred height is, for example, from0.5 to 1 cm at a cell density of below 400 cell/inch², and from 1 to 3cm at a cell density of 400 cell/inch².

Because all the valves of the cyclone device 24 (cf. FIG. 1) are closed,the level of the liquid surface at the air discharge port 42 does notrise so high.

Next, the exhaust valve 59 of the air supply device 14 is opened, andthen the control valve 69 of the cyclone device 24 (cf. FIG. 1),followed by supplying a small amount of pressurized air from the aircontrol device 18 (cf. FIG. 1) to the air duct 16 as illustrated in FIG.5 to discharge most of the slurry in the cells of the honeycombstructure 20.

Then, as illustrated in FIG. 6, pressurized air is supplied from the aircontrol device 18 (cf. FIG. 1) to the air duct 16 at an air flow of from20 to 40 m³ /minute and at a pressure of from 0.2 to 1.0 kg/cm to removeexcessive slurry which adhered to the cells in the honeycomb structure20 so that the clogging can be prevented which would otherwise occur atthe lower part of the honeycomb structure 20. Particularly preferredpressure of pressurized air in the blowing step is from 0.3 to 0.6kg/cm². The time of a single blowing operation is preferably from 0.3 to1.0 second. The blowing is carried out preferably from 1 to 3 times.

The liquid coating method and apparatus for the honeycomb structureaccording to the present invention makes it possible to coat the innercells in the honeycomb structure speedily and uniformly.

The liquid coating method and apparatus for honeycomb structureaccording to the present invention enables the coating of the innercells in the honeycomb structure without causing the liquid to adhere tothe side surface of the honeycomb structure

How, with reference to FIGS. 8 to 18b, the holding device which can beused advantageously as the holding device 22 in the above-describedembodiment will be described hereinbelow.

Here is given an example of a pipe of a shape of an elliptic cylinderhaving a major axis of 15 cm and a minor axis of 10 cm, a length of 10cm and a thickness of 5 mm.

The apparatus according to this embodiment has two main parts. One is anouter cylinder 81. The inner diameter of the outer cylinder 81 must beslightly larger than the outer diameter of the article to be held. Inthis embodiment, assuming that there is a fluctuation of ±1 cm in thesize of the article to be held, it is desirable that the outer cylinder,in the case where it has a shape of n elliptic cylinder, have an innerdiameter of no smaller than 17 cm for major axis, and no smaller than 12cm for minor axis. If the outer cylinder has a shape of a circularcylinder, its inner diameter is desirably no smaller than 17 cm. If theinner diameter is not large enough, it is difficult to insert thearticle to be held therein. Further, in the case where the article to beheld must be sealed all over its periphery, it is desirable that theouter cylinder has a length of no smaller than 21 cm. Because theholding device exhibits a weak adhesion on its ends, the cross sectionof the article to be held must be positioned sufficiently inside of thecross section of the outer cylinder of the holding device.

Another main part is a resilient tube 82, for example, a rubber tube.The inner circumference of the rubber tube 82 must be sufficientlysmaller than the outer circumference of the article to be held. On thisoccasion, if the article to be held has a shape of an elliptic column orcylinder, it may be sometimes be the case that complete sealing cannotbe established depending on the shape of the rubber tube or direction inwhich the rubber tube is fitted. In this case, it is desirable that theinner diameter of the rubber tube is sufficiently smaller than the outerdiameter of the article to be held. In this embodiment, the innercircumference of the rubber tube is desirably by at least 5 cm shorterthan the outer circumference of the article to be held. Assuming thatthe shape of the rubber tube in cross section is elliptic, the innerdiameter is desirably no larger than 13.7 cm for major axis and nolarger than 8.7 cm for minor axis. The rubber tube is attached such thatthe major axis of the rubber tube is parallel to the major axis of thearticle to be held. On the other hand, if the shape of the rubber tubein cross section is circular, its inner diameter is desirably no largerthan 8.7 cm. As for the length of the rubber tube, in this embodiment atleast 31 cm is necessary because the rubber tube is folded toward theouter cylinder and fixed thereto by means of a metal band 83. However,the method of fixing the rubber tube is not limited to theabove-described folding method. The rubber tube is preferably a tubemade of, for example, natural rubber having a thickness of from 2 to 4mm because it is excellent in resistance to wear, in contraction andexpansion properties and in resistance to chemicals.

While in this embodiment an article having a shape of an ellipticcylinder has been exemplified as the article to be held, it is obviousto one skilled in the art that the article to be held which has a shapeof a circular cylinder can similarly be held by the holding devicehaving an outer cylinder having a shape of a circular cylinder providedwith a rubber tube. Also, it is apparent that articles having a shade ofan elliptic cylinder or column of which the major axis and the minoraxis are not so different from each other, can be held by means of aholding device having an outer cylinder having a shape of a circularcylinder to which is attached a rubber tube.

As illustrated in FIG. 8, the upper and lower ends of the rubber tube 82are sealingly connected to the outer cylinder with a metal band 83 toform sealed space 84 between the rubber tube 82 and the inner wall ofthe outer cylinder 81 (cf. FIG. 9b).

The sealed space 84 communicates with the outside through a pipe 85 anda first valve 86. Further, the sealed space 84 communicates through apipe 87 and a second valve 88 with a vacuum pump 89.

The holding device according to this embodiment is actuated as follows.

Firstly, the vacuum pump 89 is not in action and, for example, the firstvalve 86 is open In this state, the sealed space 84 communicates withthe outside. The pressure in the inside of the sealed space isatmospheric pressure. As illustrated in FIGS. 9a and 9b, the diameter ofthe rubber tube 82 is small due to its elasticity, and the innerdiameter of the rubber tube 82 is smaller than the outer diameter of thearticle to be held.

Next, the first valve 86 is closed, the second valve 88 is opened, andthe vacuum pump 89 is actuated to discharge the air in the sealed space84. The discharge of the air in the sealed space 84 increases the innerdiameter of the rubber tube 82, resulting in that the rubber tube 82contacts the inner wall of the outer cylinder 81 as illustrated in FIGS.10a and 10b.

Then, an article 90 to be held is arranged in the outer cylinder 81 andthe rubber tube 82.

Next, the actuation of the vacuum pump 89 is stopped, the second valve88 is closed, and the first valve 86 is opened to make the pressure inthe inside of the sealed space 84 equal to the atmospheric pressure,thus reducing the inner diameter of the rubber tube 82 so that thearticle to be held can be held due to the elasticity of the rubber tube82 (cf. FIGS. 12a and 12b).

If desired, pressurized air supply means (not shown) may be connected tothe first valve 86 and the pressure of the inside of the sealed space ismade no lower than the atmospheric pressure to increase the holdingforce (cf. FIGS. 13a and 13b).

In order to release the holding, the pressure in the inside of thesealed space 84 may be decreased by using the vacuum means 89 andactuating it in reversed order of procedures in the embodimentillustrated in FIGS. 8 to 13, the outer cylinder has a shape of anellipse in cross section, and when the pressure in the inside of thesealed space 84 formed between the resilient tube 82 and the outercylinder 81 is atmospheric pressure, the resilient tube 82 is connectedto the outer cylinder 81 so that the central hole in the resilient tube82 can be of a shape of an ellipse as illustrated in FIG. 9a.

Instead of the above-described construction, in the variationillustrated in FIGS. 14a and 14b, the outer cylinder has a shape of anellipse in cross section, and the resilient tube is connected to theouter cylinder so that the central hole in the resilient tube can form acircle. Further, in the variation illustrated in FIGS. 15a and 15b, theouter cylinder has a shape of a circle in cross section, and theresilient tube is connected to the outer cylinder so that the centralhole in the resilient tube can form an ellipse. Still further, in thevariation illustrated in FIGS. 16a and 16b, the outer cylinder has ashape of a circle in cross section, and the resilient tube is connectedto the outer cylinder so that the central hole in the resilient tube canform a circle.

As illustrated in FIG. 8, in the case where the above-described holdingdevice is used as a holding device for the liquid coating apparatusillustrated in FIG. 1 and the like, for example, the pipe 85 and theouter cylinder 81 are connected to each other with a flexible tube 82.In order to increase sealing performance of the sealing element betweenthe lower part of the holding device and the upper wall 38 of the innertank 28 (cf. FIG. 1), and the sealing element between the upper part ofthe holding device and the lower wall 64 of the air duct 16, a flangeportion may be formed on each of the lower and upper parts of theholding device so that the flange portions can contact the upper wall 38and the lower wall 64 through the rubber tube.

FIGS. 17a, 17b, 18a and 18b illustrate as a comparative example, amongothers, a conventional method in which air is forcibly introduced into arubber tube having a inner diameter sufficiently larger than the outerdiameter of the article to be held. In the conventional method, wrinklesoccur usually at three or four places, thus indicating that completesealing of the outer wall is difficult.

As described above, according to the holding apparatus and method of thepresent invention, articles having shapes and sizes with certainfluctuation can be held firmly.

Further, according to the holding apparatus and method of the presentinvention, the article to be held and the resilient tube in the holdingdevice contact each other without causing wrinkle in the resilient tube,thus preventing the fluid, for example, a liquid for coating only theinside of the article to be held, from flowing in the axial directionbetween the article to be held and the resilient tube.

Because the resilient tube closely contacts the article to be held uponthe holding, the liquid will not flow though between the article to beheld and the resilient tube nor adhere to the outside surface of thearticle to be held when it is intended to coat the liquid only to theinside of the article to be held.

Furthermore, according to the present invention no power is requiredduring the holding, and even if the resilient tube is damaged, airpiping is damaged or outfitted, the article to be held continues to beheld. Therefore, the holding apparatus and method of the presentinvention are highly safe.

During the holding, power is unnecessary, which makes it possible toseparate the holding device and move it. Therefore, the presentinvention gives much freedom in the designing of machinery.

As described above, the holding device of the present invention can beused advantageously as a sealing device in place of the holding devicefor use in the liquid coating apparatus according to the above-describedembodiments.

EXAMPLES AND COMPARATIVE EXAMPLES Example 1

A honeycomb structure was used which was made of a ceramics having ashape of a circular cylinder of a diameter of 93 mm and a height of 75mm, having a cell density of 300 cells/inch².

As the liquid for coating, slurry was used which is composed mainly ofplatinum, aluminum oxide, cerium oxide, acetic acid, a defoaming agentand water. The specific density of the slurry was 1.55 g/ml. The solidcontent was 46.08%.

Using the apparatus exactly as illustrated in FIG. 1, theabove-described honeycomb structure as described above was set betweenthe liquid storage tank and the air duct using the holding device.

The amount of the slurry retained in the liquid storage tank and theamount of pressurized air to be supplied by the air supply device areadjusted so that the slurry was able to be pushed upward to a level ofabout 2 cm above the upper end surface of the honeycomb structure, andafter retaining the system under these conditions for one second aftercompletion of the supply of the pressurized air from the air supplydevice, pressurized air at a pressure of 3.7 kg/cm² was supplied intothe air duct for 2 seconds to completely expel the slurry which remainedin the cells. Thereafter, pressurized air at 0.37 kg/cm² was suppliedinto the air duct for 0.5 second, with interruption for 1 second, andagain pressurized air at 0.37 kg/cm² was supplied into the air duct for0.5 second.

Twenty honeycomb structures thus treated were measured for recording theamount of the slurry which adhered to the honeycomb structure and thetime required for the coating.

The weight of the slurry which adhered to the honeycomb structure was onaverage 116.2 g, and as indicated in Table 1, fluctuation A of theamount of the slurry which adhered was 5.00% as 30%. The time T requiredfor the operation was 25 seconds/number of article.

Comparative Example 1

The same honeycomb structure and slurry as used in Example 1 were used.

The honeycomb structure was completely dipped in the slurry charged inthe storage tank, taken out from the slurry, and passed below air knifejetting high-pressure air to blast off the slurry remaining in thecells.

Twenty honeycomb structures thus obtained were measured for recordingthe fluctuation A in the amount of the slurry Which adhered to thehoneycomb structure and the time T required for the coating. Table 1shows the results.

Example 2

A honeycomb structure; as used which was made of a ceramics having ashape of an ellipse in cross section of a major axis of 5.78 inch and aminor axis of 3.03 inch, a height of 2.25 inch, having a cell density of400 cells/inch².

The coating was carried out with other conditions being the same asthose in Example 1.

Twenty honeycomb structures thus obtained were measured for recordingthe fluctuation A in the amount of the slurry which adhered to thehoneycomb structure and the time T required for the coating. Table 1shows the results.

Comparative Example 2

The same honeycomb structure as used in Example 2 was coated in the samemanner as in Comparative Example 1.

Twenty honeycomb structures thus obtained were measured or recording hefluctuation in the amount of the slurry which adhered to the honeycombstructure and the time T required for the coating. Table 1 shows theresults.

                  TABLE 1                                                         ______________________________________                                                                     Adherence to                                             Fluctuation A                                                                            Time T*)  Side Wall                                        ______________________________________                                        Example 1 5.0%          25 sec/n No                                           Comparative                                                                             7.3%         100 sec/n Yes                                          Example                                                                       Example 2 3.3%          25 sec/n No                                           Comparative                                                                             8.9%         100 sec/n Yes                                          Example                                                                       ______________________________________                                         Note:                                                                         *)"sec/n" indicates seconds/number of article.                           

Example 3

A honeycomb structure was used which was made of a ceramics having ashape of an ellipse in cross section of a major axis of 3.03 inch and aminor axis of 2.25 inch, a height of 2.25 inch, having a cell density of400 cells/inch².

The coating was carried out under the same conditions as in Example 1,and then calcined in an electric oven at 400° C. for 1 hour.

Then, Fluctuation B in the amount of the catalyst components carried oneach part of the honeycomb structure was measured as follows.

An upper 1/3 part of the honeycomb structure was divided into threeparts so that a diameter is divided into three equal parts asillustrated in FIG. 7. The maximum value of the contents of catalystcomponent (% by weight) among the three parts was defined as C_(MAX),the minimum as C_(MIN), and an average of the whole values as C_(AVE),then, the fluctuation B (%) of the amount of the catalyst componentcarried being represented by the following formula:

    B=100×(C.sub.MAX -C.sub.MIN)/C.sub.AVE

The fluctuation B measured as described is shown in Table 2.

Comparative Example 3.

The same honeycomb structure as that in Example 3 was coated andcalcined under the same conditions as in Comparative Example 2; and thenfluctuation B was measured as described above.

The fluctuation B measured as described above is shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                     Fluctuation B                                                    ______________________________________                                        Example 3      1.8%                                                           Comparative    14.0%                                                          Example 3                                                                     ______________________________________                                    

Example 4

The same apparatus as illustrated in FIG. 8 to 13b was used.

Upon the practice of the procedures, an elliptic cylinder made ofstainless steel was used as the outer cylinder, which had an innerdiameter of 170.0 mm for major axis and 130.0 mm for minor axis, and aheight of 270.00 mm. The rubber tube 82 used was one made of naturalrubber, having an inner diameter of 95.0 mm, a thickness of 3.0 mm, anda length of 370.0 mm. Two pipes 85 and 87 each provided with a valvewere attached to the outer cylinder. One of the pipes was connected tothe vacuum pump 89. As the article to be held, there was used a ceramicshoneycomb of a shape of an elliptic column having an outer diameter of143.0 mm for major axis and 98.0 mm for minor axis, and a height of116.6 mm.

The section of the rubber tube 82 was expanded and the rubber tube 82was set in the outer cylinder 81, and the folded portion was fixed tothe outer cylinder 81 with the metal band 83.

The valve 86 for air release was closed, the valve 88 for the vacuumpump was opened, and the vacuum pump 89 was energized. As a result, therubber tube 82 was expanded. On this occasion, a protrusion was providedaround the air inlet port so that the inlet port could not be clogged.

The article to be held was inserted in the rubber tube in a directionsuch that the major axis of the outer cylinder was parallel with themajor axis of the article to be held, the vacuum pump was stopped, thevalve 86 for air release was opened. Then, the rubber tube contracted tohold the article.

Further, using the holding device of the above-described size articleshaving an outer diameter of from 98.0 to 140.0 mm for major axis andfrom 98.0 to 100.0 mm for minor axis and the outer wall were able to beheld under the conditions where the outer wall was completely sealed.

Example 5

Upon the practice of the procedures, a circular cylinder made ofstainless steel was used as the outer cylinder, which had an innerdiameter of 115.2 mm an outer diameter of 165.2 mm, and a height of270.0 mm. As the rubber tube was used one made of natural rubber, havingan inner diameter of 95.0 mm, a thickness of 3.0 mm, and a length of370.0 mm. Two pipes each provided 85 and 87 with a valve were attachedto the outer cylinder. One of the pipes was connected to the vacuumpump. As the article to be held, there was used a ceramics honeycomb ofa shape of a circular cylinder having an outer diameter of 118.4 mm, anda height of 150.0 mm.

In the same manner as in Example 4, the section of the rubber tube wasexpanded and the rubber tube was set in the outer cylinder, and thefolded portion was fixed to the outer cylinder with the metal band. Theoperation was in the same manner as in Example 4.

Using the holding device of the above-described size, articles having anouter diameter of from 100.0 to 140.0 mm and the outer wall were able tobe held under the conditions where the outer wall was completely sealed.

We claim:
 1. A liquid coating apparatus for coating inner cells in ahoneycomb structure with a liquid, comprising:a liquid storage tank forstoring a liquid to be used for coating, said storage tank having anupper opening and an air discharge outlet; a holder for holding ahoneycomb structure connected to the upper opening of the storage tank;an air duct for supplying an air stream via an upper opening connectedto an air supply, the air duct having a lower opening into a top of theholder for holding the honeycomb structure; a first sealing elementformed by the holder connecting a bottom of the holder to the upperopening of the liquid storage tank and a second sealing element formedby the holder connecting the top of the holder to the lower opening ofthe air duct; and means for raising a liquid in the liquid storage tankthrough the upper opening and the inner cells in the honeycombstructure.
 2. The liquid coating apparatus as claimed in claim 1,wherein said holder has a shape of a circular cylinder provided with acylindrical inner hole, said holder being separable into two halves. 3.A liquid coating apparatus for coating a liquid on walls of inner cellsin a honeycomb structure, comprising:a liquid storage tank comprising afirst tank sealed from the outside and a second tank which is insidesaid first tank, said second tank having an upper opening which isadapted to communicate with a bottom of a honeycomb structure and acommunication opening which communicates with a lower part of the firsttank; and an air supplier connected to an upper part of the first tankfor supplying pressurized air thereto.
 4. A holding apparatus forholding an article, comprising:an outer cylinder in the form of a pipehaving an inner wall with an inner diameter which allows an article tobe held to pass therethrough easily and which has a sufficient strength;a resilient tube having an inner diameter which prevents the article tobe held from passing therethrough under no tension and having ends eachsealingly connected to the outer cylinder, said resilient tube thusdefining together with the inner wall of the outer cylinder a sealedspace therebetween, means for supplying a fluid to the sealed space; andmeans for discharging the fluid from the sealed space.
 5. A holdingapparatus according to claim 4, wherein said means for supplying a fluidto the sealed space comprises a vacuum pump and outside air.
 6. A liquidcoating apparatus for coating a liquid onto inner cells of a honeycombstructure, comprising:an air duct having a lower opening, an air inletport located at a top portion of the air duct as well as an air supplyfor providing air through said air inlet port; a liquid storage tank forstoring liquid to be used for coating, the storage tank having a topopening and a bottom opening into a liquid supply means, an airdischarge outlet on one side of the liquid storage tank and an inlet onthe opposite side which is connected to a means for raising the liquidin the liquid storage tank; and a honeycomb structure having inner cellsand provided with a top and bottom portion, in which the top portion isconnected to the lower opening of the air duct via a first sealingelement while the bottom portion is connected to the top opening of theliquid storage tank via a second sealing element.
 7. A liquid coatingapparatus according to claim 6, wherein the first and second sealingelements are formed by a holder for holding the honeycomb structure. 8.A liquid coating apparatus according to claim 6, wherein the liquidstorage tank comprises a first tank inside a second larger tank,whereinthe first tank has an upper end forming the top opening into thebottom portion of the honeycomb structure, a lower end opening into thesecond larger tank and an air discharge outlet on one of the sides ofthe first tank, and the second tank has a bottom opening into a liquidsupply and an inlet on a side thereof which is connected to a means forraising liquid in the liquid storage tank through the lower end of thefirst tank into the inner cells of the honeycomb structure.